1. Field of the Invention
The present invention relates to a printing apparatus such as a laser printer for generating bitmap data from print data and printing the bitmap data, and an image processing method.
2. Description of the Related Art
There have been popularly used conventional printing apparatuses of a type which receives data (print data) associated with print contents and print formats from a host computer, generating bitmaps in a memory (this operation will be called rendering hereinafter) on the basis of the print data, and outputting (shipping) the bitmaps from the memory to an printing engine to print the bitmaps on, e.g., a paper surface.
When rendering and shipping are simultaneously performed in a printing apparatus of this type to process complicated print data and a large quantity of print data, the rendering time is much longer than the bitmap transfer time required in shipping. As a result, shipping cannot be properly performed (this phenomenon will be called a print overrun hereinafter).
To prevent this print overrun phenomenon, there is also available a printing apparatus of a type which renders a one-page output bitmap and then performs shipping. In this case, a memory for storing the one-page bitmap must be required, and the capacity of the memory must be increased in a printing apparatus having a high output resolution. As a result, efficiency of memory usage becomes poor, and the apparatus itself is very expensive.
An alternative conventional printing apparatus is also available in which one page is divided in small units (bands), shipping is performed upon completion of rendering one band, and the next band is rendered simultaneously with shipping. This operation is called banding process. In this case, when the rendering time of the next band simultaneously performed with shipping is longer than the shipping time of the preceding band, the print overrun phenomenon also occurs.
The present invention has been made to eliminate the conventional drawbacks described above, and has as its object to provide a printing apparatus and image processing method, which can minimize the capacity of a memory and prevent the print overrun.
In order to achieve the above object, according to the present invention, if an overrunning band is present while the number of band memories to be used is counted, the overrunning band is supposed to be pre-rendered, and a new band memory is assured to prepare rendering schedules. Of all the prepared schedules, a schedule having the minimum memory capacity is selected, and printing is performed.
Alternatively, if an overrunning band is present, it is supposed to be rendered, compressed, and stored in advance, and schedules are then prepared. In preparing the schedules, the expansion time of the compressed band is regarded as the rendering time. Of all the prepared schedules, a schedule having the minimum memory capacity is selected, and printing is performed.
Another object of the present invention is to provide a printing apparatus for rendering band image data to a band memory and outputting the band image data from the band memory simultaneously comprises:
time prediction means for obtaining a necessary rendering time of each band;
schedule means for preparing a rendering schedule having a minimum memory capacity on the basis of the necessary rendering time and a necessary printing time of the rendered band image data; and
rendering means for rendering each band in accordance with the schedule; and
output means for outputting contents of each band memory in accordance with the schedule.
The schedule means preferably prepares a plurality of different schedules, determines as the schedule having the minimum memory capacity a schedule having a minimum number of band memories of the plurality of different schedules, adds a new band memory for rendering, in advance, a given band whose rendering end time does not match output start time when rendering and output of image data of the given band are simultaneously performed using a predetermined number of band memories, and prepares the plurality of different schedules by changing the predetermined number of band memories.
Alternatively, the schedule means preferably prepares a plurality of different schedules, determines a schedule having a minimum memory capacity of the plurality of different schedules, adds a new memory for rendering, compressing, and storing, in advance, a given band whose rendering end time does not match output start time when rendering and output of image data of the given band are simultaneously performed using a predetermined number of band memories, and prepares the plurality of different schedules by changing the predetermined number of band memories.
In addition, the time prediction means preferably accumulates rendering times in units of objects included in each band to predict the rendering time of each band.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.